1. Field of the Invention
The present invention relates generally to an alignment method and apparatus applied to a worktable of a semiconductor dicing machine, and more particularly to a wafer alignment method and apparatus of a dicing machine, which cuts a semiconductor wafer (a workpiece) into squares with a pair of cutting blade units.
2. Description of Related Art
The processing speed of the dicing machine has become higher, whereas the diameter of the semiconductor wafer has become larger. To reduce the processing time, a cutting speed is raised, a return speed is raised, or an alignment speed is raised. Raising the cutting speed, however, may deteriorate the cutting performance, and raising the return speed excessively increases the vibrations of the dicing machine. Thus, raising the cutting speed and the return speed does not achieve dramatic results, and therefore, the best way is raising the alignment speed.
FIG. 7 is a transitional view showing the conventional alignment method. According to FIG. 7, a camera (an imaging means) of low magnification searches a pattern at a position 1 in proximity to the center O of the wafer W in FIG. 7(A), and at a position 2 a small distance away from the position 1, the camera searches the same pattern as the pattern at the position 1, and rotates the wafer in a direction .theta. with a rotational driving mechanism to perform the first rough alignment. Then, the camera searches a pattern at a position 3 in proximity to the outer circumference of the wafer W, and rotates the wafer W with the rotational direction driving mechanism to complete the rough alignment.
Next, the camera is switched to the high magnification. The camera searches a pattern at a position 4 in FIG. 7(B) and searches a pattern at a position 5. Then, the wafer is rotated in the direction .theta. to complete the alignment at a channel (CH) 1.
Thereafter, the channel is switched to a channel (CH) 2, and the wafer W is rotated by 90.degree.. The camera searches a pattern at a position 6 in FIG. 7(C) and searches a pattern at a position 7. The rotation of the wafer in a direction .theta. completes the fine alignment at CH2, and the alignment of the wafer W is completed. Then, a pair of cutting blade units cut the wafer W.
The conventional wafer alignment method, however, has a problem in that the alignment cannot be performed at high speed since the patterns at the positions 1, 2 and 3 must be imaged at three stages.
The conventional wafer alignment method has another problem in that it takes a long time to align the wafer since the camera must be moved in the direction X from the position 4 to 5 at CH1 and the camera must be moved in the direction X from the position 6 to 7 at CH2.